#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#include <sys/wait.h>
#include <arpa/inet.h>
#include <sys/socket.h>

#define BUF_SIZE 30

void error_handling(char* message);
void read_childproc(int sig);

int main(int argc, char* argv[])
{
    //套接字相关
    int serv_sock, clnt_sock;//用于服务端的套接字，用于客户端连接的套接字
    struct sockaddr_in serv_addr, clnt_addr;
    socklen_t clnt_adr_sz;

    //接收字符串的缓冲区
    char buf[BUF_SIZE];
    int str_len;

    //信号处理相关
    pid_t  pid;
    struct sigaction act; 
    int state;

    if(argc != 2)
    {
        printf("Usage : %s <port>\n", argv[0]);
        exit(1);
    }

    //信号注册
    act.sa_handler = read_childproc;
    sigemptyset(&act.sa_mask);
    act.sa_flags = 0;
    state = sigaction(SIGCHLD, &act, 0);

    //socket()创建socket
    serv_sock = socket(PF_INET, SOCK_STREAM, 0);
    if(serv_sock == -1)
        error_handling("socket() error\n");

    //bind()分配ip和端口
    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_addr.sin_port = htons(atoi(argv[1]));

    if(bind(serv_sock, (struct sockaddr*)&serv_addr, sizeof(serv_addr)) == -1)
        error_handling("socket() error\n");
    
    //listen()转换成服务端socket
    if(listen(serv_sock, 5) == -1)
        error_handling("listen() error\n");
    
    while(1)
    {
        clnt_adr_sz = sizeof(clnt_addr);
        clnt_sock = accept(serv_sock, (struct sockaddr*)&clnt_addr, &clnt_adr_sz);
        if(clnt_sock == -1)
            continue;
        else 
            puts("new client connected \n");
        
        //创建子进程
        pid = fork();
        if(pid == -1)//创建失败
        {
            close(clnt_sock);
            continue;
        }
        if(pid == 0)//子进程运行区域
        {
            close(serv_sock);
            while((str_len = read(clnt_sock, buf, BUF_SIZE)) != 0)
                write(clnt_sock, buf, str_len);

            close(clnt_sock);
            puts("client disconnected...\n");
            return 0;
        }
        else//父进程运行区域
            close(clnt_sock);
    }
    close(serv_sock);
    return 0;
}

void read_childproc(int sig)//回收子进程
{
    pid_t pid;
    int status;
    pid = waitpid(-1, &status, WNOHANG);
    printf("removed proc id : %d \n", pid);
}

void error_handling(char* message)
{
    fputs(message, stderr);
    fputc('\n', stderr);
    exit(-1);
}
